Hydraulic metering device

ABSTRACT

The metering device for a liquid medium comprises a cylinder and a piston operatively disposed therein to define a metering chamber ahead of the piston. The outlet end of the cylinder is open and closed by an evacuation valve. The piston is driven forwardly through a working stroke to force the liquid medium in the metering chamber out of the chamber and past the evacuation valve. A check valve located in the metering chamber moves from a closed to an open position on each working stroke to preclude entrapment of air in the metering chamber and thus provide for more accurate metering. The metering device may include means to regulate the length of the working stroke.

RELATED APPLICATIONS

This is a divisional of U.S. patent application Ser. No. 10/664,094,filed 17 Sep. 2003 now U.S. Pat. No. 7,118,352.

BACKGROUND OF THE INVENTION

This invention relates to a metering device for the precision feeding ofa liquid medium, even in relatively small or minute quantities.

Oil lubricants are among the many liquids that are at times metered. Ina given instance, the feeding of too little oil may place a machine atrisk. However, too much oil may contaminate a product and contribute topollution. Thus, accuracy in metering can be very important.

While accuracy in metering is generally desired, it is often difficultto attain. Air often gets into a feeding or metering system and becomesentrapped in the metering chamber. The entrapped air in the meteringchamber will displace liquid medium in the measured quantity to rendermetering in minute quantities virtually impossible and in largerquantities inaccurate. It is generally an object of this invention toprovide a metering device for a liquid medium wherein entrapment of airin the metering chamber is generally precluded to provide for moreaccurate metering even in minute quantities.

SUMMARY OF THE INVENTION

The invention resides in a metering device for a liquid medium and whichcomprises a housing having an inlet and an outlet for the liquid medium.A cylinder is disposed in the housing and has an open end thatcommunicates with the housing outlet. Check valve means are provided inthe housing and are biased to close the open end of the cylinder. Apiston is operatively disposed in the cylinder and forms therewith ametering chamber ahead of the piston. Means are provided to conduct theliquid medium from the inlet to the metering chamber. Means are furtherprovided to drive the piston forwardly through a working stroke to forcethe liquid medium in the metering chamber out of the chamber and pastthe check valve means toward the housing outlet. The piston breaks theplane of the open end of the cylinder on each working stroke togenerally preclude entrapment of air in the metering chamber and thusprovide for more accurate metering of the liquid medium, even in minutequantities.

The present invention comprises an improvement of the metering devicesas described and claimed in U.S. Pat. Nos. 4,784,578 and 4,784,584,incorporated herein by reference.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cut-away side view of a first embodiment of the presentinvention.

FIG. 2 is an exploded view of the embodiment depicted in FIG. 1.

FIG. 3 is a fragmentary cut-away side view of the upper end of theembodiment depicted in FIG. 1.

FIG. 4 is a fragmentary view of the upper end of a second embodiment ofthe present invention.

FIG. 5 is an overhead, cross-sectional view of a valve used in thepresent invention presented along line 5-5 of FIG. 2.

FIG. 6 is an overhead, cross-sectional view of a second valve used inthe present invention presented along line 6-6 of FIG. 2.

FIG. 7 is an overhead, cross-sectional view of a third valve used in thepresent invention presented along line 7-7 of FIG. 2.

FIGS. 8-13 show the flow of a liquid being regulated by the presentmonitoring device.

FIG. 14 is a fragmentary cut-away side view of a third embodiment of thepresent invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Although the disclosure hereof is detailed and exact to enable thoseskilled in the art to practice the invention, the physical embodimentsherein disclosed merely exemplify the invention that may be embodied inother specific structure. While the preferred embodiment has beendescribed, the details may be changed without departing from theinvention, which is defined by the claims.

Referring to the drawings, wherein like numerals represent like partsthroughout the views, there is generally designated at 10 a hydraulicmetering device. Referring more specifically to FIGS. 1-3, inclusive, ofthe drawings, the hydraulic metering device 10 of this invention isintended to be disposed in a liquid medium supply line. A pump, notshown, delivers the liquid medium to the metering device 10 in pressurepulses for metered flow to a user assembly, also not shown.

Still referring to FIGS. 1-3, the hydraulic metering device 10 has threesections including a pair of opposed hollow cap fittings 11 and 12 and amain body 13, with the main body further comprising a cylindricalchamber 14. The hollow cap fittings 11 and 12 further comprise an inlet15 and outlet 16, respectively. The inlet 15 and the outlet 16 each areadapted to communicate with a fitting such as a conventionalpipefitting. As shown in the drawings (see FIG. 1), the inlet 15 andoutlet 16 may be axially aligned with the chamber 14 and to each other.A pair of o-rings, 17 a and 17 b, provide a liquid-tight seal betweenthe cap fittings 11 and 12 and the main body 13.

The main body 13 includes a check valve 44, a piston 29 and anevacuation valve 21. The evacuation valve 21 acts as a type of checkvalve in the present invention. However, for clarity of presentation theevacuation valve 21 and the check valve 44 are described in thespecification and represented in the drawings as distinct elements. Thehydraulic metering device 10 has three springs. The springs are termedthe piston return spring 34, the evacuation seal spring 24 and thedetent spring or check valve spring 54. The check valve 44 togglesbetween a closed and open position. The evacuation valve 21 is opened bypressure of the liquid within the chamber ahead of the piston 29 and isheld open by the piston crown to preclude the introduction of any airinto the system.

A cylindrical sleeve 18, integral with body 13, is disposed in thechamber 14 generally adjacent to the outlet 16 and in axial alignmentwith the chamber 14. The end of the sleeve 18 adjacent to the outlet 16is tapered to provide a peripheral edge 20 that projects forwardly inthe direction of the outlet 16 at the inside diameter of the sleeve 18.

At the peripheral sleeve edge 20, an evacuation valve member 21 providesclosure for the end of the sleeve 18. The evacuation valve member 21comprises a carrier 22 that is axially slidable in the decreaseddiameter portion 23 of chamber 14 and is biased to the sleeve closureposition shown in FIG. 1 by the evacuation seal spring 24 extendingbetween the shoulder 25 adjacent to the outlet 16 and the shoulder 19 ofa carrier 22. Facing the sleeve 18 and generally centrally thereof, thecarrier 22 is provided with a cylindrical resilient sealing block 26.The sealing block 26 is seated in a carrier recess 27 and is engagedupon the sleeve edge 20 to effect closure of the sleeve end. Theperiphery of the carrier 22 is provided with one or more flats 28 asshown in FIG. 7, so that the interior of the cylinder sleeve 18 isplaced in communication with the outlet 16 when the evacuation valvemember 21 is open.

In an alternate embodiment, evacuation valve member 21 and sealing block26 are integrally formed in a one-piece construction. The one-piecemember may be formed from a plastic such as polypropylene or any othersuitable material.

A piston 29 is operatively disposed within the cylindrical sleeve 18 andforms therewith the piston or metering chamber 30 as shown in FIG. 1 tobe forward of the piston 29. Another o-ring seal 17 c provides aliquid-tight seal about the periphery of the piston 29 (see FIG. 2).Externally the piston 29 is stepped, providing an annular shoulder 31intermediate its length (see FIG. 3).

The exploded view of FIG. 2 further illustrates details of the meteringdevice 10. As previously noted, the fittings 11 and 12 are threadinglyengaged with the body 13, thereby forming an airtight device. Theo-rings 17 a and 17 b also contribute to the airtight nature of themetering device 10. The elements of the fittings 11 and 12 may bearranged and secured separately to the body 13. For example, theevacuation valve 21 and the evacuation seal spring 24 may be removedfrom the body 13 without it being necessary to remove the piston 29, thecheck valve 44, or the piston return spring 34.

Referring specifically to FIG. 3, a fragmentary view of the upper end ofthe metering device 10 is shown. Another annular shoulder 33 is adjacentto the rear end of the stepped piston 29. The annular shoulder 33 on thepiston 29 provides an abutment for the piston return spring 34 disposedbetween the shoulder 33 and the shoulder 32 formed at the junction ofsleeve 18 and chamber 14. The piston 29 has a drive end portion, whichextends rearwardly from the shoulder 33 and is longitudinally slidablealong the cylindrical wall of chamber 14. The chamber 14 is described asbeing cylindrical, but any solid-shaped chamber, such as hexagonal oroctagonal, that allows the system to operate is allowable. In thissense, the use of a cylindrical chamber would encompass all such shapedchambers. As shown in FIG. 6, the piston drive end portion 35 isprovided with one or more flats 36 so that pressure will be equalized onopposite sides of the piston portion.

The forward face of the check valve assembly 44 carries a resilientcylindrical sealing block 45 that is seated in the recess 46 (see FIGS.2 and 3). The sealing block 45 is selectively engageable with the entryto a passageway or through bore 37 of the metering piston 29 toselectively close the through bore 37. A pair of passageways 39 isformed above shoulder 31 thereby permitting liquid communication betweeninner cavity 38 and chamber 14.

In an alternate embodiment, resilient cylindrical sealing block 45 isreplaced with a spherical ball. A mating cylindrical seat is formed inthe entry to through bore 37. While any suitable material could be used,in the preferred alternate embodiment, the spherical ball is stainlesssteel. Its preferred diameter is ⅛ inch and is designed to protrude 1/32inch from the check valve 44.

The piston drive end portion 35 defines an inner cavity 38 (see FIGS. 1and 3) in which the check valve assembly 44 is seated. The forward faceof the check valve assembly 44 carries the projecting resilientcylindrical sealing block 45 mounted in the valve member recess 46. Thesealing block 45 is in alignment with and engageable with the passageway37. Within the inner cavity 38, an annular detent 50 is formed about itsinner periphery 51. The check valve 44 includes a diametrically disposedpassageway 53 extending there through. Detent spring 54 is positionedwithin the passageway 53. A pair of detent ball members 55 is biasedoutwardly by the spring 54. The outward pressure exerted upon the ballmembers 55, in conjunction with the location of the annular detent 50,defines two distinct positions for the check valve 44: open and closed.FIGS. 1 and 3 depict the valve 44 in the closed position.

In a second embodiment 10 a shown in FIG. 4 and a third embodiment shownin FIG. 14, an adjustment device 70, such as a set screw or thumb screw71, is disposed in a threaded inlet aperture 72 generally central of aninlet 15 a in an alternate cap fitting 11 a. As shown in the Figures theinlet 15 a may be perpendicular to the piston 29 and the chamber 30. Inthe alternate embodiments 10 a, 10 b, an adjustment stem adapter 73,including a packing nut 74 and o-ring 75, is provided to form aliquid-tight seal about the screw 71 and threaded aperture 72. Aretaining clip 76 may also be provided near screw end 77 to prevent theaccidental removal of the screw 71. When the screw 71 is fully retractedfrom the chamber 14, the upper surface 48 of check valve member 44 willhave the capability of being biased against the screw end 77 to providefor a piston chamber 30 of maximum length for maximum feeding of liquidmedium with each working stroke of the piston 29. As the set screw 71 isturned to project inwardly from the wall 52, the piston chamber 30 willbe correspondingly shortened and provide for corresponding feeding ofliquid medium with each piston stroke. The amount of feeding is not onlycontrolled by the size of the piston chamber 30, but also by the pulsingrate of the pump, not shown.

In the alternate embodiment 10 a shown in FIG. 4, the detent spring 54and the detent ball members 55 of the first embodiment are replaced withdiametrically opposed leaf spring or leaf springs 154. The leaf spring154 may be centrally located with respect to the check valve member 44and the piston chamber 30. The leaf spring 154 is secured to the checkvalve assembly 44 by a snap ring 156. The ends of the leaf spring 154located away from the center of the check valve member 44 are nestledinto detents 158 located in the piston 29, which limit the range ofmotion of the check valve member 44. Thus, the leaf spring 154 has ashape and angle that permits the check valve member 44 to move between afully closed position and a fully opened position (shown in phantom).

As shown in FIG. 5, the upper surface 48 of the check valve member 44 isprovided with one or more flats 47 to provide for the passage of liquidmedium around the valve member. FIG. 6 shows the upper surface of thedrive end portion 35 of the piston 29 with flats 36. The flats 36 alsocontribute to an even flow of liquid through the bore 37. When the checkvalve member 44 is nested within the piston 29 (see FIG. 2), the flats44 are not aligned with the flats 36. Such an arrangement allows liquidflow to continue past the check valve member 44 through the bore 37.FIG. 7 shows the upper surface of the carrier 22 with flats 28 andhaving sealing block 26 centrally located within the carrier 22. Carrier22 also assists in an even liquid flow through the metering device. Theutility of these devices will become more evident as hereinafter furtherdescribed with reference to FIGS. 8-13.

Operation

The operation of the FIG. 1 embodiment of the metering device 10 isshown in FIGS. 8-13, inclusive. The general steps of the device are asfollows:

Position 1: The check valve 44 is closed, no pressure is coming from thepump (not shown), and the metering chamber 30 is full of liquid. (FIG.8)

Position 2: The check valve 44 is still closed; there is now pressurefrom the pump forcing the piston 29 downward and onto sealing block 26.The downward pressure is greater than the resilience of the evacuationseal spring 24, and sealing block 26 unseats and liquid flows past thesealing block 26. (FIGS. 9 and 10)

Position 3: The bottom of the piston 29 continues to press down on thesealing block 26 allowing the purge function to occur. The spring forceof the piston return spring 34 overcomes the force of the check valvespring 54 and the check valve 44 snaps open. (FIG. 11)

Position 4: Once the pressure bleeds off, the piston 29 retracts and thesealing block 26 reseats. The metering chamber 30 refills at top ofstroke, and the check valve spring 54 snaps the check valve 44 closed.(FIGS. 12 and 13).

Detailed Operation

A liquid pressure pulse from a hydraulic pump, not shown, initiates apower or working stroke of the piston 29, as detailed in FIG. 8. Duringthe working stroke, initially the piston 29 and the check valve 44 inits closed, forwardly projecting position move together as a unit.Liquid enters through the inlet 15. When the pressure in the pistonchamber 30 exceeds the biasing force of the evacuation seal spring 24,the evacuation valve member 21 opens to allow the liquid medium contentin the piston chamber 30 to escape toward and through the outlet 16 (SeeFIG. 9).

Toward the end of the working stroke of the piston 29, the lowermostsurface of the piston 29 engages with the upper surface of theevacuation sealing block 26 thereby further biasing carrier 22 andspring 24 (see FIG. 10). At the end of the working stroke of the piston29, the check valve 44 remains closed, as generally shown in FIG. 10,such that the valve is not permitted to expose or open the check valve44 to the liquid medium in the chamber 14 behind the piston 29.

As shown in FIG. 11, at the termination of the pressure pulse, theevacuation valve 21 is biased to closure again by the evacuation sealspring 24 as the piston 29 commences its return stroke in response tothe lower surface of shoulder 21 a of the evacuation valve 21shouldering on the upper surface 12 a of the outlet cap fitting 12.Simultaneously, the combined forces from the shouldering, detent spring54 and piston return spring 34 cause the check valve 44 to move from itsclosed position to its open position. (See FIG. 12) At the conclusion ofthe return stroke of piston 29, travel of the check valve 44 isinterrupted by engagement of the valve 44 with the end wall 52 (FIG. 13)or adjusting screw 71 (FIG. 14). At this point, the check valve 44 snapsclosed. The piston 29 meanwhile continues afterward to its initialposition. The metering device 10 is then ready for the next cycle ofoperation.

The use of the adjusting screw 71, as shown in FIG. 14, allows anoperator to increase or decrease the volume of liquid media delivered bythe device lob. The screw 71 may be adjusted to heights that may differby only a few mils. Such a precise adjustment is advantageous inlubrication systems, where only a few drops of lubricating liquid arenecessary for lubrication.

A preferred embodiment of the above process is next discussed in moredetail and with reference to FIGS. 8-13, inclusive. When the pistonreturn spring 34 is fully compressed it exerts a force of 4.89 pounds.Using standard spring manufacturing tolerances of +/−10%, the forcecould range from 4.40 to 5.38 pounds. The purpose of this spring 34 isto return the piston 29 to top dead center (TDC) (either end wall 52 orscrew end 77) after the metering device 10 has dispensed a predeterminedamount of liquid. The geometry of the assembly requires 90 to 110 psi ofinlet pressure to compress the spring 34.

When the evacuation seal spring 24 is fully compressed in the assembly,it exerts a force of 6.53 pounds. Using standard spring manufacturingtolerances of +/−10%, the force could range from 5.88 to 7.18 pounds.The purpose of this spring 24 is to create a biasing mechanism for theevacuation seal 26. The geometry of the assembly requires 120 to 147 psiof inlet pressure to compress the spring 24.

When the check valve spring 54 is fully compressed in the assembly, itexerts a force of 1.90 pounds. Using standard spring manufacturingtolerances of +/−10%, the force could range from 1.71 to 2.09 pounds.The purpose of this spring 54 is to exert a force on the balls 55 thatcreate the biasing mechanism on the check valve 44. The geometry of theassembly requires 35 to 43 psi (pounds per square inch) of inletpressure to compress the spring 54. It is to be understood that while acompression spring is the preferred spring for the check valve, a leafspring 154 could also be utilized, as described above with reference toFIG. 4.

The preferred embodiment requires approximately 210-270 psi of fluidpressure to get the piston 29 to initiate movement. Approximately210-257 psi is the sum of the pressure to overcome the force of thepiston return spring 34 and the evacuation seal spring 24. The devicerequires approximately 245-300 psi of pressure to get the check valve 44to ride over the critical pressure point, with 245-300 psi being the sumof the piston return spring 34, evacuation seal spring 24 and checkvalve spring 54. The preferred embodiment requires 210-257 psi toshoulder the piston 29 against the positive stop at bottom dead center(BDC). Pressure from the supply pump continues to increase to thepredetermined system bypass pressure. When the supply pressure is shutoff, the system begins to bleed off. The piston 29 stays at BDC untilthe supply pressure bleeds off to 210-257 psi.

As the pressure continues to bleed off, the evacuation seal 26 andpiston 29 return at the same rate until the evacuation seal 26 contactsthe sleeve edge 20. Once contact is made with the sleeve edge 20, thepiston 29 and evacuation seal 26 stop. The evacuation seal 26 stopsbecause it is shouldered against the sleeve edge 20. The piston 29 stopsuntil the pressure bleeds off to 90-110 psi at which point the pistonreturn spring 34 continues to move the piston 29 toward top dead center(TDC) (either end wall 52 or screw end 77).

Once the piston 29 breaks away from the evacuation seal 26, theremaining upstream pressure is introduced into the pump chamber. At thispoint, the pressure is acting on the evacuation seal 26, which is biasedby the evacuation seal spring 24. The evacuation seal spring 24 forcemust be enough to keep the seal 26 closed. If not, the upstream liquidcould leak through and allow a secondary surge of lubricant to bedispensed from the metering device 10.

As the piston 29 approaches TDC, the check valve 44 contacts its stop52. At this point, the piston return spring 34 must have a spring forcehigh enough to overcome the 1.90 pounds from the check valve spring 54and move the check valve 44 over the critical pressure point and readyto meter for its next cycle.

The above spring values do not have to be exactly as explained above forthe device to operate. The values may be increased or decreasedproportionately depending upon the purpose of the meter. However, twovery important features with any spring combination must be designedaccordingly. First, the evacuation seal spring must have a higher springforce than that of the piston return spring. This prevents the secondarysurge of liquid. Second, the piston return spring force as it approachesTDC must be greater than the check valve spring force. This insures thatthe check valve will move over the annular detent and ready the meterfor its next cycle.

According to the several embodiments hereinbefore described, theinvention provides for a more accurate metering device. Should any airget into a liquid medium supply system that includes the metering deviceof this invention, such air should create no problem. Since each workingstroke of the piston 29 breaks the plane of the open end of the cylinderby a predetermined distance, the metering chamber 30 is completelyvoided or purged with each stroke leaving no air for entrapment todisturb the accuracy of the metering device. In a preferred embodiment,the predetermined distance is 0.0314 inches.

With the metering device of this invention, even minute quantities ofliquid medium can be accurately metered. Various modes of carrying outthe invention are contemplated as being within the scope of thefollowing claims particularly pointing out and distinctly claiming thesubject matter regarded as the invention.

The foregoing is considered as illustrative only of the principles ofthe invention. Furthermore, since numerous modifications and changeswill readily occur to those skilled in the art, it is not desired tolimit the invention to the exact construction and operation shown anddescribed. While the preferred embodiment has been described, thedetails may be changed without departing from the invention, which isdefined by the claims.

1. A metering device for a liquid medium, the metering devicecomprising: a housing having an inlet and an outlet for said liquidmedium, said housing including a first chamber having an open endcommunicating with said outlet; a first check valve means in saidhousing, said first check valve normally biased to close said open endof said first chamber; a first piston having a drive end, said firstpiston slidably received and operatively disposed in said first chamber,said first piston and said first chamber defining a metering chamber;means to conduct said liquid medium from said housing inlet to saidmetering chamber; a second check valve located in said housing, receivedand operatively disposed in said first piston drive end and moveablebetween and including at least a first position and a second position,whereby pressure from said liquid medium moves said second check valve;said first piston forcing said liquid past said first check valve meansto completely evacuate said metering chamber on each working stroke ofsaid first piston to thereby generally preclude entrapment of air insaid metering chamber; and an adjustment mechanism, said adjustmentmechanism regulating the length of said working stroke of said firstpiston to regulate the volume of said liquid within said meteringchamber.
 2. The metering device of claim 1 wherein the adjustmentmechanism comprises a screw.
 3. The metering device of claim 1 whereinsaid first check valve means includes a seal normally biased and insealing engagement with said open end of said first chamber.
 4. Themetering device of claim 1 wherein said second check valve meanscomprises a spring biased toggle mechanism arranged to provide selectivepositioning of said second check valve means.
 5. The metering device ofclaim 4 wherein said second check valve means further comprises adiametrically disposed passageway including a detent; at least onedetent ball member; and a check valve spring, said check valve springbiasing said at least one detent ball member outwardly against detent toprovide said selective positioning of said second check valve means. 6.The metering device of claim 4 wherein said second check valve comprisesa helical spring.
 7. The metering device of claim 4 wherein said secondcheck valve comprises a leaf spring.
 8. The metering device of claim 1wherein said first piston extends a predetermined distance out of saidcylindrical chamber to completely evacuate said metering chamber.